Paddle card with improved performance

ABSTRACT

A paddle card construction disclosed for use in connecting electronic devices together. The paddle card takes the form of a circuit board that has a plurality of conductive contact pads arranged thereon in pairs. The contact pads of each pair are spaced apart from each other to provide a pair of points to which cable wire free ends may be terminated, such as by soldering. The spacing of the pads apart from each other in effect reduces to amount of capacitance in the cable wire termination area on the circuit board, thereby reducing the impedance and insertion loss in that area at high frequencies. The contact pads of each pair may be further interconnected together by a thin, conductive trace that extends lengthwise between the contact pads.

RELATED APPLICATIONS

This Application is a Divisional Application of U.S. application Ser.No. 13/745,352, filed Jan. 18, 2013, which is incorporated herein byreference in its entirety.

BACKGROUND OF THE PRESENT DISCLOSURE

The Present Disclosure relates, generally, to cable interconnectionsystems, and, more particularly, to improved cable assemblies for use inhigh speed data transmission applications.

Conventional cable interconnection systems are found in electronicdevices, such as routers, servers and the like, and are used to formsignal transmission lines. These transmission lines may extend betweenchip members and connectors, connectors in two different devices, andbetween devices themselves. Most often, differential signal wires areused for each such transmission line in a cable and, although it is easyto maintain a desired impedance profile along the length of the cabledue to the cable geometry, it is difficult to maintain such a profilewhere the wire ends are terminated to a circuit board or paddle card.The wires are terminated to contact pads that are disposed on a surfaceof the circuit board. In such a situation, the exterior insulation isstripped back and the bare conductors are terminated to solder pads orthe like. The contact/solder pads are elongated and are generallyrectangular in shape, with one pad being associated with only one wire.This type of termination always has impedance discontinuities associatedwith it.

The Present Disclosure is therefore directed to a circuit board, orpaddle card, for use with a cable assembly particularly suitable forhigh speed data transmission applications, and which includes animproved termination area that reduces the impedance discontinuity whichoccurs with the termination of cable wires to elongated rectangularcontact pads located on the paddle card.

SUMMARY OF THE PRESENT DISCLOSURE

Accordingly, there is provided an improved paddle card having animproved termination structure which promotes beneficial termination inhigh speed data transmission applications.

In accordance with an embodiment described in the Present Disclosure, acable assembly is disclosed that utilizes a specially configured circuitboard, or paddle card, to which the wires of the cable are terminated.Instead of conventional elongated, rectangular contact pads, the circuitboard termination area for each single wire of the cable assembly isformed with two distinct contact sections associated with each signalwire of the cable. In one embodiment, the two contact pads for each wireare spaced apart from each other lengthwise along the circuit board. Inanother embodiment, the two contact pads for the wire are spaced apartfrom each other, but are connected by a thin trace extending lengthwisebetween the two pads, the width of the connecting trace being a fractionof the width of the contact pads, so that when viewed from above thiscontact pad arrangement has a “dogbone” configuration.

The use of two contact pads in place of one elongated contact padreduces the overall area of the termination structure for each wireterminated to the circuit board. Preferably, the two contact pads arespaced apart by an intervening spacing equal to or greater than that ofone of the contact pads. The elimination of this extra conductivesurface area reduces the capacitance, as compared to a regular,elongated rectangular contact pad, thereby reducing the impedancediscontinuity that normally occurs in transition from the structuredorder of the cable wires to their termination on the surface of thecircuit board. This modification of the impedance profile is importantin that the circuit board termination area is prone to crosstalk, andflattening out the impedance discontinuity curve gives the cable andconnector structure a better impedance profile and results in reducedcrosstalk and electrical noise. In one of the embodiments of the PresentDisclosure, the total length of the two contact pads may range betweenabout 0.5 to about 0.8 of the total length between exterior ends of thecontact pads. Similarly, the contact pads are preferably separated by anintervening distance of between about 20% to about 40% of the totallength between the opposing edges of a pair of the contact pads.

These and other objects, features and advantages of the PresentDisclosure will be clearly understood through a consideration of thefollowing detailed description.

BRIEF DESCRIPTION OF THE FIGURES

The organization and manner of the structure and operation of thePresent Disclosure, together with further objects and advantagesthereof, may best be understood by reference to the following DetailedDescription, taken in connection with the accompanying Figures, whereinlike reference numerals identify like elements, and in which:

FIG. 1 is a perspective view of a paddle card style circuit board withwires of a cable assembly terminated thereto;

FIG. 2 is a top plan view of the structure illustrated in FIG. 1;

FIG. 3 is an enlarged top plan view of a one of the contact pads and awire terminated thereto in the assembly of FIG. 2;

FIG. 4 is a top plan view of one embodiment of the termination area ofan improved circuit board constructed in accordance with the principlesof the Present Disclosure;

FIG. 5 is a top plan view of another embodiment of the termination areaof FIG. 4;

FIG. 6 is an enlarged perspective view of the cable wire-terminationarea of a circuit board incorporating the principles of the PresentDisclosure utilizing a construction of the termination area of FIG. 4;

FIG. 7 is a diagram of an impedance plot through a connector system,with a multi-wire cable on the right side thereof, then the terminationarea of the cable wires adjacent it, the connector mating interface andthe device connector termination to a circuit board on the left sidethereof;

FIG. 8 is a simulated impedance plot taken from a model that compares anordinary cable termination utilizing a singular rectangular contact padas shown in FIG. 3 and labeled “Standard” to an improved cabletermination area utilizing the dual contact pads arrangement inaccordance with the Present Disclosure shown in FIG. 4, labeled “New;”

FIG. 9 is a simulated insertion loss plot taken from a model comparingan ordinary cable termination utilizing a singular rectangular contactpad as shown in FIG. 3 and labeled “Standard” to the improved dualcontact pad termination area shown in FIG. 4, labeled “New;” and

FIG. 10 is an actual impedance plot comparing the impedance through anordinary cable termination utilizing a single, rectangular contact padas illustrated in FIG. 3 to an improved dual contact pad terminationarea of the type illustrated in FIG. 4, with their plots respectivelylabeled “Standard” and “New.”

DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the Present Disclosure may be susceptible to embodiment indifferent forms, there is shown in the Figures, and will be describedherein in detail, specific embodiments, with the understanding that thePresent Disclosure is to be considered an exemplification of theprinciples of the Present Disclosure, and is not intended to limit thePresent Disclosure to that as illustrated.

As such, references to a feature or aspect are intended to describe afeature or aspect of an example of the Present Disclosure, not to implythat every embodiment thereof must have the described feature or aspect.Furthermore, it should be noted that the description illustrates anumber of features. While certain features have been combined togetherto illustrate potential system designs, those features may also be usedin other combinations not expressly disclosed. Thus, the depictedcombinations are not intended to be limiting, unless otherwise noted.

In the embodiments illustrated in the Figures, representations ofdirections such as up, down, left, right, front and rear, used forexplaining the structure and movement of the various elements of thePresent Disclosure, are not absolute, but relative. Theserepresentations are appropriate when the elements are in the positionshown in the Figures. If the description of the position of the elementschanges, however, these representations are to be changed accordingly.

FIGS. 1-3 illustrate a conventional cable assembly used to connectmulti-wire cables to circuit boards house within connector housings inorder to provide a connector. Typically, a connector 10 of a plug stylehas a protective outer connector housing with a hollow termination endthat receives an end of a multiple-wire cable 14 and, at its oppositeend, a smaller mating connector end. The mating end of the connectorholds a mating blade, shown as a circuit board, or paddle card, 15 in anorientation suitable for mating with an opposing, mating receptacleconnector (not shown) that has a slot which receives the forward end ofthe circuit board 15. In order to provide a means for ensuringengagement with the opposing connector after mating with it, theconnector may be provided with a latch member that mates with thehousing of an opposing connector.

FIG. 1 is a perspective view of a conventional termination structureused to connect the individual wires 25 of the cable 14 to individualcircuits on the circuit board 15, which takes the form of a paddle card.As shown, the cable 14 encloses a plurality of wires 25, and the signalwires thereof illustrated are of the twin-ax construction, with signalconductors 27 running lengthwise and the conductors 27 are spaced apartfrom each other. The inner signal conductors 27 are surrounded by anouter insulative covering 26. Free ends 28 of the signal conductors 27extend forwardly past the leading ends of the wire insulative coverings26. The insulative covering 26 is typically itself enclosed by an outershield member 29, which is shown in FIGS. 1- 2 as a braided wire, butwhich may take the form of a conductive shield formed from a copper foilor the like.

Turning to FIG. 2, which is a plan view of the termination structureshown in FIG. 1, it can be seen that the circuit board 15 takes thegeneral form of a rectangle and has opposing leading and trailing edges20, 22. The leading edge 20 is the forwardmost edge of the circuit board15, or to the left in FIG. 2, and is that portion of the circuit board15 inserted into the card-receiving slot of an opposing, matingconnector, not shown. In this regard, the circuit board 15 is typicallyformed with an array of conductive mating contacts 21 arranged thereonwhich mate with terminals of the opposing mating connector. Similarly,the trailing edge 22 of the circuit board 15 defines a termination areawhere the free ends 28 of the cable wire signal conductors 27 areterminated to the circuit board 15. In order to accommodate all of thewires, the circuit board 15 has an array of termination structures, eachtaking the form of a single contact pad 23. These contact pads arearranged in a pattern proximate to the trailing edge 22 of the circuitboard 15.

In termination, the free ends 28 of the cable wire signal conductors 27are exposed by removing a given length of their outer covering 26, andthe outer shield member 29 also has a portion of it removed. Drain wires30 may be provided in the cable and are associated with each of thetwin-ax pairs of wires. They are separately attached to the circuitboard, either by direct attachment or by way of a cradle (not shown),and connected to an internal ground plane layer of the circuit board 15.As illustrated, the wire free ends 28 are attached to the termination(rearmost) contact pads 23 by a suitable method such as soldering, andin such an attachment method, the solder not only contacts the contactpad 23, but also creates a fillet alongside the body of the wire freeends 28 which runs the length of the termination contact pad 23 on bothsides of the wire free end 28.

Due to the ordered structure of the wires 25 in the cable 14, it isrelatively easy to maintain a desired impedance profile throughout thelength of the cable 14. Twisted pair wires are commonly used to transmitdifferential signals and are most commonly used in high-speed electricaltransmission cables. These signal cables have one or more twisted pairsof wires that are twisted together along the length of the cable, witheach such twisted pair being encircled by an associated groundingshield. These twisted pairs typically receive complimentary signalvoltages, i.e., one wire of the twisted pair will carry a +1.0 voltsignal, while the other wire of the twisted pair will carry a −1.0 Voltsignal. The wire pairs are twisted together along the axis of the cableso that each of the wires extends in a helical path along the cable andthe wires are spaced apart from each other the same distance along thishelical path for the length of the cable. The impedance of twisted pairtransmission cables may be very easily controlled at a desired level,because it is relatively simple to maintain a specific geometry orphysical arrangement of the signal conductors and the grounding shield.However, an impedance change will usually be encountered in the areawhere the cable is mated to a connector, or a circuit board that is partof a connector.

This ordered structure of the cable ends where the transition from thecable 14 to the circuit board 15 occurs, namely, at the cabletermination area, as the wires 25 of each pair of twin-ax wires 25 arefirst untwisted, and subsequently moved apart from each other andsoldered to their associated contact pads 23. A typical impedanceprofile of a structure, such as the known one illustrated in FIG. 1,which uses a cable connector mating to a receptacle connector located inan electronic device, is illustrated in FIG. 7, which displays theimpedance discontinuity that occurs through the connector system. FIG. 7illustrates the ordered geometry of the cable 14 at A, to the area wherethe free ends 28 of the cable wires 25 are untwisted at B, and then tothe area where the termination of the wire free ends 28 to the circuitboard (or paddle card) 15 occur at C. Following further through theconnector system, from right to left in FIG. 7, the area where thecircuit board 15 mates with an opposing connector, namely, the connectorinterface area is shown at D and this area is followed by the transitionarea at E where the receptacle connector is itself connected to circuittraces of the circuit board in the electronic device.

Area A plots the transmission cable, which because of its orderedgeometry, has a constant baseline impedance of about 100 ohms. It isdesirable to try to maintain this constant value through the connectorsystem. Such a tolerance cannot be maintained and hence, designersattempt to keep the discontinuities down to at least a +/−10% of the 100ohm baseline value, and as low as +/−5% of the 100 ohm baseline. In areaB, the twisted pair wires are spread apart in order to align them withthe termination contact pads 23 and this movement causes a rise in thesystem impedance as shown. Next, the wire free ends are terminated tothe termination contact pads 23, which results in a drop of theimpedance as at C. Then, in the area where the two connectors mate, theimpedance rises in area D and then the impedance returns to its baselinevalue of 100 ohms in area E, where the signal transmission path islargely encompassed within a circuit board. Keeping the impedancediscontinuity, i.e., the peaks and valleys shown in FIG. 7 to no morethan a 10% deviation from the baseline reduces crosstalk and noise.

It has been discovered that the impedance discontinuity may becontrolled in the cable wire termination area to meet the 10% tolerancetarget and lower, in a simple, cost-effective manner. A manner ofaccomplishing this involves interrupting the traditional rectangularstructure of the termination contact pads 23 by eliminating a portion ofthe contact pads. Such a structure is illustrated in FIGS. 4-6, where itcan be seen that the formerly elongated rectangular contact pads 23 witha length of L have been replaced by a pair of spaced-apart contact pads23 a and 23 b which have respective lengths of L1 and L2.

This length L extends from the leading edge 40 of the forwardmostcontact pad 23 a in FIGS. 4-5 to the trailing edge 41 of the rearmostcontact pad 23 b. The pair of contact pads 23 a, 23 b are preferablyaligned with each other lengthwise along the circuit board 15 so thattheir sides edges are coincident, as noted by the dashed lines in FIG.5. The total length of the pair of contact pads 23 a, 23 b is L3, whichis the sum of the two lengths, i.e., L1+L2, which, as illustrated, isless than L. The lengths L1 and L2 may vary in accordance with the gaugeof the cable wires 25, and will be a percentage of L. Good results havebeen obtained in circuit boards utilizing the following lengths: L1=0.8mm, L2=0.8 mm and L=2.6 mm, meaning that the intervening spacing thatseparates the two contact pads 23 a, 23 b is equal to 1.0 mm. With suchdimensions, L3 is equal to about 0.61 L.

The width, W of the contact pads above, are all constant and preferablywill not vary among the contact pads. In the example set forth above,the contact pads 23 a, 23 b have had a width of 0.7 mm. Such a dimensionensures enough room on the pad for the solder attachment, the cable wirefree end and also provides enough area for adhesion to the circuitboard. As such, the width of the contact pads will be a constant andonly the length of the contact pads will vary, based upon the particularapplication. However, it will be understood that some applications willdictate increasing or decreasing the width of the contact pads and todate it is believed that 0.5 mm is about the smallest width which can beused and still have enough area to receive a via 50, as explained tofollow.

It is believed that the advantages described herein with respect to thePresent Disclosure will also be attainable with L3/L ratios of 1.6/2 or1/2 in instances where the total length is about 2.0 mm or L1 and L2 areabout no more than 0.5 mm. In these instances, L3 will vary from about0.5 L to about 0.8 L. Similarly, the intervening spacing between thecontacts pads 23 a, 23 b of each pair of pads can preferably range frombetween about 0.2 L and about 0.4 L with a preferred length being about1.0 mm. Hence, it is preferred that L3 can range from about 0.5 L toabout 0.8 L. The contact pads 23 a, 23 b, as illustrated, may takeeither a square or a rectangular configuration. The contact pads 23 a,23 b may further include vias 50 that extend into the circuit board 15.One via 50 may be provided for each contact pad of the pair of contactpads 23 a, 23 b as shown in the bottom portion of FIG. 4, or the via 50may be disposed in either the forwardmost contact pad 23 a or therearmost contact pad 23 b. The use of the vias 50 may be beneficial tothe circuit board design in that it can provide an anchoring point forits associated contact pad, increasing its resistance to removal, orpeel strength.

In another embodiment of the Present Disclosure and as illustrated inFIG. 4, the two contact pads 23 a, 23 b may be preferably interconnectedby a thin conductive connecting trace 23 c that extends between the twocontact pads 23 a, 23 b. The placement of the trace 23 c may be anywherebetween the side edges of the contact pads and preferably, the trace 23c is centered between the side edges so that the wire free end 28 mayextend along it and so the trace provides a coupling path for the wire.In this orientation, the connecting trace 23 c mirrors the extent of theexposed signal conductor in its extent on the surface of the circuitboard. In testing, connecting traces 23 c having widths of about 0.2 mmhave been used with contact pads 23 a, 23 b having widths of about 0.7mm with suitable results. With such a structure, the elimination of themetal area between the contact pads but for the connecting trace resultsin an overall plate reduction of about 27% as compared to the full platehaving dimensions of L×W. It is believed that using two contact pads,with or without the connecting trace, with dimensions that reduce themetal plate area between about 25% to about 40% will provide the desiredresults. In other words, it is desirable to reduce the contact pad areaby at least about 60% to at least about 75% from the full plate area ofL×W.

The forwardmost contact pads 23 a, 23 b of each pair of cable wires 25may include conductive transmission traces 43 that define transmissionlines leading from the termination contact pads to the mating contactsof the circuit board 15. While the contact pads 23 within each wire pairare separated by a first spacing, the transmission traces 43 areseparated by a second spacing, and in the embodiment illustrated, theyconverge toward each other such that the second spacing therebetween isless than the first spacing between the termination contact pads 23.

The use of two contact pads 23 a, 23 b for each cable wire 25termination as opposed to one long contact pad reduces the amount ofmetal used in the termination area and lessens the plate area, whichconsequently reduces the capacitance of the connector system in thetermination area. This reduction results in an increase in the impedancein the wire termination area. This has the effect of raising theimpedance discontinuity curve in area C of FIG. 7, thereby bringing theimpedance closer to the baseline impedance for the system. FIG. 8 is animpedance plot of a simulation through a modeled cable and terminationarea that covers areas A-C of FIG. 7. The impedance of a standard wiretermination, that is, utilizing an elongated contact pad 23 asillustrated in FIG. 3 is shown as “Standard,” and in the form of adashed line. The impedance of a wire termination to two contact pads 23a, 23 b is illustrated as “New,” and takes the form of a dashed-dottedline. It can be seen that there is about a 6 ohm improvement in the newtermination vs. the standard conventional style termination, raising theimpedance from 86 to 92 ohms, easily achieving and bettering a +/−10 ohmtolerance for this part of the connector system.

A similar simulation plot of the two termination system is shown in FIG.9, but which illustrates the insertion loss achieved. As shown in FIG.9, the insertion loss is predicted to improve as the frequency increasesand this improvement is modeled around 0.5 dB at 20 Ghz. FIG. 10 is anactual impedance plot comparing a standard termination of a connectorsystem as illustrated in FIG. 1 to one in accordance with the PresentDisclosure as illustrated in FIG. 4. The termination of both connectorsystems is shown at “A” on their respective plots and it can be seenthat our improved termination reduces the discontinuity in this area bya significant amount, down to about 97 ohms, rather than the about 88ohms of the standard termination, leading to an improvement of almost90% in the impedance discontinuity at this location.

The Present Disclosure is not limited to the above-describedembodiments, and may be changed and modified in various ways based onthe gist of the Present Disclosure, and these changes and modificationsshould not be eliminated from the scope of the Present Disclosure asdefined by the appended claims.

What is claimed is:
 1. A circuit board for use in a high speed cableconnector, the circuit board having improved impedance characteristics,comprising: a circuit board having opposite leading and trailing edges,the circuit board including a first portion proximate to the trailingend defining a termination area in wires of an associated cable areterminated, and a second portion extending forwardly from and spacedapart from the first portion and ending proximate to the second portion,the second portion including a plurality of contacts disposed thereonand configured to mate with an opposing connector, the first portionincluding a plurality of termination contact pads disposed on a surfacethereof, the termination contact pads being arranged in pairs of contactpads, the contact pads of each pair of termination contact pads beingarranged on the circuit board so that a leading edge of the forwardmostpad of the contact pad pair and a trailing edge of the rearmost pad ofthe contact pad pair are separated by a predetermined terminationlength, L, for a single one of the cable wires, and the contact padsbeing separated from each other by an intervening spacing, and thecumulative length of the contact pads is between about 0.5 L to 0.8 L.2. The circuit board of claim 1, wherein each contact pad has a squareconfiguration.
 3. The circuit board of claim 1, wherein each contact padpairs include a thin, conductive trace interconnecting the pads of eachcontact pad pair together such that the contact pad pairs have adogbone-like configuration when viewed from the top.
 4. The circuitboard of claim 3, wherein the interconnecting conductive trace isgenerally centered between the contact pads it interconnects and atleast one of the contact pads includes a via extending into the circuitboard.
 5. The circuit board of claim 3, wherein the interconnectingconductive trace has a width between about 25% and about 40% of thewidth of one of the contact pads.
 6. The circuit board of claim 1,wherein the pairs of contact pads are spaced apart widthwise by a firstspacing and conductive traces extending forwardly from the forwardmostcontact pads are separated by a second widthwise spacing, less than thefirst spacing.
 7. The circuit board of claim 1, wherein each contact padhas a length of about 0.8 mm and the intervening spacing has a length ofabout 1.0 mm.
 8. The circuit board of claim 1, wherein the interveningspacing between the contact pads has a length of between about 0.2 L toabout 0.4 L.